Taper Bearings

Terms For Tapered Bearings Cone The cone assembly consists of the the rollers (A), the cage (B) and the inner ring (C). The cage separates the rollers and the inner ring forms a channel, with flanges on each side, to keep the rollers in line. The cage shown here is a pressed steel window-type cage. Single row tapered roller bearings can only accept axial loads acting in one direction. Thus, there is a need for an opposing bearing set in each wheel end assembly.

Terms For Tapered Bearings Cup The outer ring of the bearing is called the cup. It provides the mating surface for the rollers to run on (or race around). This surface is thus called the race (D). The cone and cup are sold as separate elements to permit one master cone to fit several cup thicknesses.

Tapered Bearing Loading Patterns Normal loading When the bearings are installed properly, with the correct bearing pre-load, the load pattern will be symetrical (blue area). Under this condition, with proper sealing and lubrication, the bearing should easily run for the life of the truck.

Tapered Bearing Loading Patterns Improper Loading Overtightening the adjusting nut, or not seating the bearing properly, causes a shift in the load pattern on the bearing surfaces. Wear becomes uneven on the roller surfaces -- roller, inner ring flange and race -- because the pressures on the surfaces are very distorted (blue area). In this situation the bearing fails prematurely.

Taper Bearings Failure Analysis The ability of this design to handle heavy radial loads and single direction thrust loads has made tapered roller bearings one of the most popular bearings. The basic tapered roller bearing consists of two separate components. The cone consists of the inner race, rollers and cage The outer ring or cup The components are specially angled or tapered to a common point known as the apex, so that all the elements can roll along the same axis. Tapered bearings can only accommodate thrust loads in one direction and are usually used in pairs such as in front inner or outer wheel bearings.

Taper Bearings Failure Analysis Typical failure modes in tapered wheel bearings include: Improper bearing adjustment (clearance not within specs) Misalignment (bearing center lines do not match) Contamination (metal, abrasive particles or moisture present) Improper lubrication ( wrong viscosity, insufficient amount, degraded lubricant) Installation damage (wrong tool, or no tool used; hammering on the bearing components) Impact loads (improper installation, severe service, hitting curbs or potholes) Other damage (poor fit, electric arcing, service fatigue)

Improper Bearing Adjustment

Alignment Proper bearing alignment When bearings are in proper alignment their center lines are parallel to each other. In most designs, the center lines of a pair of bearings should be represented by only one line.

Alignment Improper bearing alignment If the bearings are not seated properly their center lines will be at an angle to each other. This problem may be noticeable if you look closely for a flush mounted bearing surface before you remove it. Common problems that produce a cocked installation are: Dirt or burrs preventing a flush mount Outer cup installed without proper tools A warped shaft Nut faces that are out of line

Alignment Misaligment Damage Roller Damage Worn at an angle. Wear patterns of any type are not parallel with the flat ends of the rollers, it indicates that the rollers are not running true. Produced when the bearing is cocked in the housing.

Alignment Misaligment Damage Race Damage Worn on one side. When the bearing is cocked it will run crooked, creating an uneven wear pattern on both the rollers and the race. If you observe severe wear on one side of the race, but little on the other, you can be certain that something kept the bearing from being properly seated in the housing.

Effects of Contamination Roller Damage Grooves in the race. Scratch marks in the surface of the race are caused by hard particles in the lubricant. This type of damage should be a warning flag. The hard particles may be from spalling of the bearings or from the wear of some other wheel end component. If the cause is not evident, an oil analysis may be called for.

Effects of Contamination Etched metal surface Etched metal surfaces are usually the result of water contamination. The water allows oxidation and the metal becomes pitted and porous. The main sources of water contamination are a failed wheel seal or leaking hubcap.

Effects of Contamination Scored rollers Scoring around the rollers indicates contamination of the lubricant by dirt, girt or metal particles. By tracking down the nature of the dirt, through an oil analysis, it should be simple to pinpoint the cause. External contamination will show up as grit and contaminants from the environment. Internal contaminants will most likely be from worn surfaces inside the wheel end.

Improper Lubrication Flaking metal When metal appears to be flaking off across the full surface of the race, you can suspect there is a lack of proper lubrication. Lack of lubrication can be caused by simply too little lubricant present, or by breakdown of the lubricant from heat or contamination. It can also be the result of using the wrong lubricant -- type or viscosity.

Improper Lubrication Discoloration Discolored steel anywhere, on either the cup or cone, indicates overheating. This photograph shows the characteristic look of overheated steel on the outside of the cup. The primary suspect should be lack of lubrication. Low levels from missed maintenance or a leaking seal should be considered likely candidates.

Installation Damage Deformed cage The rib of this cage design has been bent out of round. Even small distortions of the assembly can destroy a bearing. This type of damage is usually the result of rough handling. Hammering on the bearing during installation is a likely cause. Excessive press fit from a distorted hub or a mis-application (wrong part number) could also produce this damage.

Installation Damage Nicks and dents Damage like this dent in the cage or retainer is the result of a sharp tool being used to install or seat the bearing. A drift or screwdriver used on a bearing is guaranteed damage.

Installation Damage Broken ring The hairline crack shown here is a break in the inner ring. The cause is excessive pressure on the bearing. It is possible that an outside shock to the wheel end could produce this break, but it would have to be so great as to leave plenty of other clues. The more likely cause is excessive interference fit (wrong size) or excessive installation pressure

Installation Damage The solution is proper training. Dented cup This is a clear example of a bad installation. Dings and dents in the outer bearing surfaces are almost always the result of attempts to install the bearing improperly. In this example, some sharp tool, likely a drift, was used to press the cup into the housing. The solution is proper training.

Impact Loads Dents in race A sharp dent, like the one shown here, is the result of a heavy blow to the wheel end. This could be the result of slamming into a pot hole, but it may also be caused by excessive installation pressure

Impact Loads Multiple dents Dents in the race caused by external impact loads may progress to spalling of the metal surface. Once the integrity of the surface is broken, wear will progress more rapidly. This photograph shows where five rollers were driven into the surface of the race. Over time the impacted areas became deeper. With this one, it was probably hard to hear the radio

Other Damage Corrosion of the outer surface Fretting corrosion of the outer surface of the bearing is often the result of a loose fitting bearing. A mis-application (wrong part number) is possible, but more likely a worn hub or spindle is to blame.

Other Damage Overheating Burnt rollers. Overheated bearing steel develops very characteristic patterns. The colors reflect the temperatures. A strawberry brown indicates a 300°F temperature and deep purple means the heat went over 700°F. The cause of overheating is lack of lubrication, over tightening during bearing adjustment, or overloading the carrying capability of the bearing.

Other Damage Spalling Fatigued metal. Spalling occurs as fatigued metal lifts off of the surface. The example pictured here is extreme, but not wholly unlikely. You may find surfaces where only small patches have begun to flake and disintegrate. Spalling will occur at the normal end of bearing life. If it occurs early, the likely causes are lack of sufficient lubrication and excessive loading.

Other Damage Arcing Electrical damage. Electric arc welding on the engine or chassis without proper grounding can destroy the wheel bearings. The electrcial charge passes through the bearing assembly and lifts off the bearing surface. There are some other electrical charges that will cause this problem (besides lightning)

Conclusion A properly trained and informed technician will have a direct bearing on the life of tapered bearings!